A diagram of a horseshoe crab is available on the Enchanted Learning website. This diagram shows both the dorsal and ventral sides of the crab.
A horseshoe crab has a shield or horseshoe-shaped prosoma, or head; a carapace; and a long, stiff tail. The prosoma has compound eyes and light receptors and protects the animal's legs, feeding pincers and gills. Horseshoe crab males are smaller than the females.
The horseshoe crab is not a crab at all but is related to scorpions and spiders. However, the horseshoe crab is harmless and does not sting. Scientists believe that horseshoe crabs have existed for about 500 million years and haven’t changed much in that time.